Microstructural, Mechanical and Antibacterial Characterization of Nanocrystalline Diamond Thin Films

Abstract

Nanocrystalline diamond thin films exhibit unusual hardness, wear resistance, and corrosion resistance properties, and are currently being considered for use in orthopaedic, ophthalmic, and other medical implants. The purpose of this study was to evaluate the hardness, Young's modulus, microscratch adhesion, and antimicrobial properties of nanocrystalline diamond thin films. Microwave plasma enhanced chemical vapor deposition (MPCVD) was used to deposit nanocrystalline diamond thin films on p-type silicon wafers. Raman spectroscopy, scanning electron microscopy (SEM), and high resolution transmission electron microscopy (HRTEM) were used to determine quality and phase purity of the nanocrystalline diamond thin films. The thin films consisted of diamond nodules that varied in morphology (size=60-600 nm). HRTEM showed that the films contained rectangular crystallites with dimensions between 2 — 4 nm. Raman spectroscopy confirmed that the thin film sample contained both tetrahedrally-bonded and amorphous carbon phases. The hardness and Young's modulus values for the nanocrystalline diamond thin films were 29.4 ± 11.9 GPa to 72.0 ± 10.7 GPa and 346.4 ± 98 GPa to 551.8 ± 71.5 GPa, respectively. Microscratch adhesion testing was performed on the nanocrystalline diamond films to examine the functional adhesion strength between the diamond films and the silicon substrates. The nanocrystalline diamond/silicon wafer systems demonstrated very good film adhesion (LCN ≈ 3.1 — 3.4 N). A CDC biofilm reactor was utilized to incubate and grow Pseudomonas fluorescens on the surfaces of the nanocrystalline diamond thin films and stainless steel coupons. Quantitative data showed that bacterial attachment on the nanocrystalline diamond thin films was quite significant and comparable to that on stainless steel surfaces. This work suggests that nanocrystalline diamond thin films are good candidate materials for biomedical implants but are susceptible to microbial colonization.